Solid state electric power usage meter and method for determining power usage
First Claim
1. A method for determining electric power usage by a load attached to an electric power network, the method comprising:
- sensing current in each phase of the electric power network;
detecting the voltage level of each phase of the electric power network;
receiving signals related to the current in each phase and signals related to the voltage on each phase;
sampling said current and voltage related signals at predetermined times at a rate where is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and converting said samples to digital signals representing said current and voltage levels at the predetermined times;
calculating instantaneous values of electric power at the predetermined times from the digital signals; and
accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network.
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Abstract
A digital solid state electric power usage meter for determining power usage by a load attached to an electric power network. The meter has a current sensor coupled to each phase of the electric power network for sensing current in each phase, a voltage divider coupled to each phase of the power network for detecting the voltage level on each phase, an analog to digital (A/D) converter coupled to the current sensors and voltage dividers receiving signals from the current sensors related to the current in each phase and signals from the voltage dividers related to the voltage on each phase. The A/D converter samples the current and voltage related signals at predetermined times at a rate which insures that samples of the current and voltage related signals do not repeat for a large number of cycles of the network frequency or never repeat and which rate is at least twice as fast as the rate of change of the current and voltage related signals and converts the samples to digital signals representing the voltage levels and current at the predetermined times. A processor calculates instantaneous values of power at the predetermined times from the digital signals and a memory accumulates the instantaneous values so as to form a value representative of electric power usage by the load attached to the network.
72 Citations
30 Claims
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1. A method for determining electric power usage by a load attached to an electric power network, the method comprising:
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sensing current in each phase of the electric power network; detecting the voltage level of each phase of the electric power network; receiving signals related to the current in each phase and signals related to the voltage on each phase; sampling said current and voltage related signals at predetermined times at a rate where is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and converting said samples to digital signals representing said current and voltage levels at the predetermined times; calculating instantaneous values of electric power at the predetermined times from the digital signals; and accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for determining electric power usage by a load attached to an electric power network, the method comprising:
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sensing current in each phase of the electric power network; detecting the voltage level of each phase of the electric power network; receiving signals related to the current in each phase and signals related to the voltage on each phase; sampling said current and voltage-related signals at predetermined times at a rate where is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and which rate is at least twice as fast as the rate of change of the current and voltage-related signals and converting said samples to digital signals representing said current and voltage levels at the predetermined times; calculating instantaneous values of power at the predetermined times from the digital signals; and accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power usage meter comprising:
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first means coupled to each phase of the electric power network for sensing current in each phase; second means coupled to each phase of the electric power network for detecting the voltage level on each phase; third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for sampling said current and voltage related signals at predetermined times and for converting said samples to digital signals representing said current and voltage levels at the predetermined times; processor means for calculating instantaneous values of power at the predetermined times from the digital signals; and means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network, and further wherein said processor means further comprises means for calculating the amount of electric power usage without implementing actual division and without incurring round-off error, said means for calculating comprising; means for implementing division by a calibration constant without performing actual division, said means for implementing division comprising means for repetitively; multiplying said voltage and current related signals together to form a product and adding said product to an accumulated sum; after each step of multiplying; subtracting said calibration constant from said sum to obtain a result; determining if said result is larger than said calibration constant, and if so, incrementing a counter; again subtracting said calibration constant from said result, and if the result of the subtraction is still larger than the calibration constant, repeating said steps of incrementing the counter, subtracting and determining as many times as necessary until said result is less than said calibration constant; when said result is less than said calibration constant, maintaining said result as a remainder in the counter; and using the count in said counter as a measure of the electric power usage.
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30. A method for determining electric power usage by a load attached to an electric power network, the method comprising:
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sensing current in each phase of the electric network; detecting the voltage level of each phase of the electric power network; sampling said current and voltage related signals at predetermined times and converting said samples to digital signals representing said current and voltage levels at the predetermined times; calculating instantaneous values of electric power at the predetermined times from the digital signals; and accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network, and further wherein said step of calculating further comprises calculating the amount of electric power usage without implementing actual division and without incurring round-off error, said step of calculating comprising; implementing division by a calibration constant without performing actual division, said step of implementing division comprising repetitively; multiplying said voltage and current related signals together to form a product and adding said product to an accumulated sum; after each step of multiplying; subtracting said calibration constant from said sum to obtain a result, determining if said result is larger than said calibration constant, and if so, incrementing a counter; again subtracting said calibration constant from said result, and if the result of the subtraction is still larger than the calibration constant, repeating said steps of incrementing the counter, subtracting and determining as many times as necessary until said result is less than said calibration constant; when said result is less than said calibration constant, maintaining said result as a remainder in the counter; and using the count in said counter as a measure of the electric power usage.
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Specification